Apparatus for electrofusion of biological particles

ABSTRACT

Apparatus and methods of use thereof are provided for fusing neutral polarizable biological bodies and sorting neutral polarizable biological bodies by imposing them to a non-uniform electric field. The dielectrophoretic effect of the non-uniform electric field will either impose variable displacements of the types of cells to facilitate sorting, or will align cells contiguously between a pair of electrodes in preparation for fusion. To fuse the cells the aligned cells are exposed to a direct current impulse.

The present invention is directed to apparatus for fusing biologicalparticles by electrical means. The present invention is further directedto apparatus for sorting biological particles by the application ofnon-uniform electric fields to such particles.

The apparatus according to the present invention may be utilized to fusebiological particles by the process of electrofusion or to sortbiological particles by the process of dielectrophoresis. The process ofelectrofusion involves exposing the biological particles, such as cells,which are to be fused to a mild non-uniform electrical field to alignthe cells between inert electrodes. Typically, a mild alternatingcurrent field of about 10 volts rms at about 250 khz may be utilized.After alignment, a short pulse of about 15 volts dc for about 50microseconds may be applied, which causes a dielectric breakdown of thecontiguous cell membranes, thereby opening a membrane channel betweenthe cell interiors of contiguous cells. The cells then fuse together.Using electrofusion, fusion yields of over 25%, and often approaching100%, may be readily obtainable, as compared to about 0.001% to 5%efficiency for classical methods of cell fusion, such as, treatment withvirus particles or polyethylene glycol. A major advantage ofelectrofusion is in its provision of a precise time of the onset offusion-related events, which may be important in the rate studies offusion-related events in cells in the fields of genetics, morphology,cell surfaces, and cell physiology.

The exposure of neutral particles, particularly biological particlessuch as cells, to non-uniform electric fields induces a dipole in eachparticle. If dc current is not applied to fuse the cells, then thedivergent non-uniform nature of the field results in one end of thedipole being in a region of higher field strength than the other andthis effect causes the dipole to be pulled in the direction of theincreasing field. Therefore, non-uniform electric fields can inducetranslational and rotational motion of biological particles insuspension. This motion has been defined as dielectrophoresis. Thesemotions can be used to characterize and separate biological particles,such as living cells and parts thereof. Apparatus utilizing thedielectrophoresis phenomenon are described in my U.S. Pat. Nos.3,162,592 and 4,326,934.

It is therefore an object of the present invention to provide improvedapparatus for electrofusion of cells which are convenient, versatile andadaptable for handling a high number of biological particles per unittime.

It is a further object of the present invention to provide apparatus forsorting cells by dielectrophoresis which may handle a large number ofcells per unit time.

These and other objects will become readily apparent from the followingdescription and claims.

FIG. 1 is a block diagram for one embodiment of circuitry for theparticle sorter application of a disk chamber according to the presentinvention.

FIG. 2 is a perspective cross-section of a disk chamber embodiment ofthe present invention.

FIG. 3 is an expanded view of the concentric grooved electrode shown inFIG. 2.

FIG. 4 is a cut-away view of the top plate assembly shown in FIG. 2.

FIG. 5 is a diagram of one embodiment of an electrical circuit for usewith a linear chamber fuser according to the present invention.

FIG. 6 is a perspective view of a linear chamber fuser according to thepresent invention.

FIG. 7 is an expanded view of a portion of the linear chamber fusershown in FIG. 6.

FIG. 8 is an expanded view of the electrode connection to the cell ofthe linear chamber fuser of FIG. 6.

One embodiment of the present invention comprises a disk chamber whichincludes a set of parallel electrodes at least one of which is providedwith concentric circular grooves. When the electrodes are spaced apartand supplied with an ac voltage the sharp edges of the grooves provide anon-uniform electric field. This field may either be used to align cellsin preparation for later fusion by a dc (or ac) pulse or may be used tosort and characterize biological cells by dielectrophoresis. Thedielectrophoresis sorting technique may be used, for example, todistinguish biological particles such as cells by age, abnormalities,history and culture media, hemophilic traits, and the like.Dielectrophoresis may also be utilized to separate mixtures ofbiological cells by type or by physiological condition. The disk chamberaccording to the present invention may be advantageously used to sortbiological cells with the rates up to about 10 million cells per minute.

Referring to FIG. 1 there is shown a block diagram of a preferredelectrical circuit for sorting biological particles. The electrodes tobe utilized in the dielectrophoresis process are illustrated by chamber10. The biological cells are injected into chamber 10 through injector11 which mixes cells incoming from infusion pump 12 and from the fluidreservoir 13 which provides the fluid in which the cells are suspended.The sorted cells are collected in the stream-splitting means 14.However, in the case of the disk chamber according to the presentinvention the electrodes 10 also serve as the stream-splitter since thecells are collected in the grooves on the surface of one of theelectrodes. Various electrical devices may be utilized to regulate theinput frequency and voltage to the electrodes. As shown, the electrodes10 are regulated by a frequency synthesizer 15, PET computer 16 and SWTPcomputer 17 which analyzes data observed by television monitor 18.Computer 17 may also be equipped with a disk storage 19, an XY plotter20 and a printer 21.

Referring to FIG. 2 there is shown a perspective cutaway view of apreferred disk chamber cell sorter and cell fuser according to thepresent invention. Referring to FIG. 2 the disk chamber is defined bylower electrode plate 30 and upper transparent electrode plate 31. Plate31 is partially coated with conductive layer 33. The electrodes 30 and31 are parallel and spaced apart at a convenient distance to applyappropriate nonuniform electric fields to cells within the chamber.Typically the spacing between electrodes 30 and 31 will be about 500micrometers. Electrode 30 has surface 32 into which is cut a pluralityof concentric or spirally placed grooves which form sharp edges. Thegrooves are concentric or approximately concentric about entrance inlet34. Electrodes 30 and 31 are insulated from each other by insulationring 35 and insulating O-rings 36. Upper plate assembly 37 is assembledto the lower electrode plate 30 and legs 38 by a plurality of bolts 39and 39A. Cells which are able to traverse the entire radius within thechamber are collected and withdrawn through exit port 40 and may eitherbe discarded or recycled back into the chamber. The lower electrode 30may be electrically connected (not shown) to an electrical terminal. Theupper electrode 33 may also be connected to an electrical terminal andis accessible to such connection through a cut-out 41 in upper plate 37which exposes a portion of electrode 31.

Referring to FIG. 3 there is shown an enlarged view of the grooveshaving sharp points which are cut into the electrode surface ofelectrode 30.

Referring to FIG. 4 there is shown an expanded view of the cut-out 41 intop plate 37 which provides an accessible opening for electricalconnection to electrode 31 and conductive undercoating 33.

In a typical operation of the apparatus shown in FIG. 2, a stream ofbiological particles, such as cells, is admitted through port 34 intothe chamber defined by electrodes 30 and 31. The biological cells tendto flow, carried by the moving stream, radially and outwardly from theopening in port 34. The frequency and intensity of the ac voltageapplied to the electrodes may be varied so that the cells which aredesired for collection will arrive at a predetermined radial distancefrom the opening of port 34, then later collected and withdrawn throughexit port 40 when the field is relaxed. The exit port 40 may beconnected to a detection device (not shown) which may electronicallyconvert the detection device output signal to a concentration value toprovide a measure of the total quantity of cells passing through exitport 40. Exit port 40 may also be connected to a pump means (not shown)for moving the stream of particles through the chamber.

It will be noted that no special treatment of the biological particlesprior to sorting is necessary other than to have them suspended in aproperly isoosmotic medium of low ionic conductivity. However, thepossibility of using special chemicals to modify cellulardielectrophoretic behavior is not precluded and may even be desirable inorder to increase the sorting capabilities of the device.

An alternative use of the device shown in FIG. 2 is as an electrofusiondevice whereby a low ac voltage is applied to electrodes 30 and 31 inorder to allow the cells to contiguously align between the electrodes.Typically a mild ac field of about 10 volts rms at about 250 khz may beutilized. Then a brief pulse of about 10 to about 250 volts dc for about50 microseconds may be applied to cause fusion of the aligned cells. Inthis manner, a large number of cells may be handled for electrofusion.

It is realized that the frequency, voltage and duration of impulsedescribed above are suggested as typical values, however, it would bewithin the skill of those of ordinary skill in the art to adjust thevarious parameters, depending on the type and size of cells which are tobe sorted or fused, the type of carrier stream utilized, the type ofchemical modification of the cells, if any, which is utilized, and thelike.

Referring to FIG. 5 there is shown a diagram of a preferred electricalcircuit for utilizing the apparatus of FIG. 2 of a second embodimentaccording to the present invention, described hereinafter as a linearchamber electrofusion device. The fusion chamber is depicted by 50 andcontains parallel electrodes 51. Typically, the course of theelectrofusion process may be observed through microscope 52, therefore,it is preferred that at least some of the fusion chamber components beoptically transparent. The biological cells within the chamber 50 arefirst aligned by an ac current provided by oscillator 53 and monitoredby oscilloscope 54. Then a short dc pulse is imposed provided byamplifier 55 and conventional commercial stimulator 56.

Referring to FIG. 6 there is shown a perspective view of a preferredlinear chamber electrofusion device according to the present invention.Referring to FIG. 6 there is shown an optically transparent base plate60 which may be, for example, a conventional glass microscope slide. Tothe base plate 60 is affixed by appropriate adhesive, opticallytransparent tubular members 61 and metallic electrode terminals 62.Tubular members 61 accommodate optically transparent linear chamber 63in which the biological particles are electrofused. The biologicalparticles and fluid support stream are conducted into and out of chamber63 by inlet and exit means 64, which are preferably stainless steeltubes. Wires 68 connect the electrodes which are located within chamber63 to terminals 62.

Referring to FIG. 7 there is shown an expanded cross-sectional view of aportion of tubular member 61 accommodating chamber 63 and tube 64. Asshown, tubular member 61 is characterized by a longitudinal hole intowhich are telescoped tube 64 (preferably, stainless steel) and opticallytransparent sleeve 65 (preferably, glass). Telescoped into sleeve 65 areoptically transparent end piece 66 and the end of chamber 63. Thecentral longitudinal orifices of end piece 66 and chamber 63 are of thesame height and width. Typically the ratios of the height of the orificeto the width of the orifice will be approximately 10:1. The width of theorifice will be a convenient dimension for accomplishing electrofusion,usually within the range of 200 to 400 microns. The transparent elements61, 65, 63 and 66 may be conveniently affixed by an appropriatetransparent adhesive. Metallic member 64 may also be affixed by aconventional adhesive, such as epoxy.

Referring to FIG. 8 there is shown a partial cutaway of an end ofchamber 63 to which one of the electrodes 67 is clipped. The electrodes67 run along the interior of chamber 63 on oppositely facing walls. Theelectrodes are long, flat, metallic wires which are flush against facingwalls within the chamber 63. At one end of chamber 63 the electrodes 67are exposed and soldered to wires 68.

In typical operation of the linear electrofusion chamber, the biologicalcells flow in an appropriately suspending fluid through one of the tubes64 into chamber 63. The terminals 62 are electrically connected to an acand dc source as shown in FIG. 5. A mild ac field in the range of about1 to 20 volts rms, preferably about 10 volts rms, at about 200 to 600kHz, typically about 250 kHz, is then applied to allow the cells toorient between the electrodes in a contiguous manner to the non-uniformelectric field. Then a brief pulse of voltage in the range of 10 to 250volts dc, typically about 15 volts dc for a period of time in the rangeof about 1 to 200 microseconds, typically about 50 microseconds, isapplied and fusion of the cells takes place within chamber 63. The fusedcells may then be withdrawn through one or both of the tubes 64. Theentire electrofusion operation may be observed by placing the slide 60under a microscope and focusing the chamber 64 for observation. Afteruse, chamber 63 and tubes 64 may be cleaned and sterilized byautoclaving and reused.

It will be appreciated that the foregoing description and specificembodiments are by way of illustration of the particular apparatusdescribed. It will be apparent, however, to those of ordinary skill inthe art that many modifications and changes in the specific apparatusmay be made without departing from the scope and spirit of theinvention.

What is claimed is:
 1. A method for fusing neutral polarizable bodiescomprising the steps ofgenerating a non-uniform electric field in achamber defined by at least two parallel and cofacially disposedelectrodes, at least one of said electrodes having a surface comprisinga plurality of substantially concentric grooves, and said chamberprovided with inlet means being centrally disposed to said grooves;introducing said bodies into said chamber through said inlet means;exposing said bodies in said chamber to said field to align saidparticles contiguously between said electrodes; imposing a directcurrent impulse to said electrodes, thereby fusing said contiguouslyaligned said bodies; withdrawing the fused bodies from said chamber. 2.A method according to claim 1 wherein said neutral polarizable bodiescomprise biological particles.
 3. A device for subjecting neutralpolarizable bodies to a non-uniform electric field for fusing or sortingof said bodies, comprising:a chamber defined by at least two paralleland cofacially disposed electrodes, at least one of said electrodeshaving a surface comprising a plurality of substantially concentricgrooves; said chamber provided with an inlet means for introducing saidbodies into said chamber, said inlet means disposed centrally to saidgrooves; whereby said bodies being introduced through said inlet meansand radially and outwardly traversing said chamber, are exposed to anon-uniform electric field induced by said grooves by an externallyapplied electric potential between said electrodes.
 4. A deviceaccording to claim 3 further comprising outlet means for withdrawingsaid bodies arriving at a predetermined radial distance from saidcentrally disposed inlet means.
 5. A device according to claim 3 whereinone of said electrodes comprises an optically transparent conductivematerial.
 6. A method for sorting neutral polarizable bodies comprisingthe steps of generating a non-uniform electric field in a chamberdefined by at least two parallel and cofacially disposed electrodes, atleast one of said electrodes having a surface comprising a plurality ofconcentric grooves, and said chamber provided with inlet means beingcentrally disposed to said grooves;introducing said bodies into saidchamber through said inlet means; outwardly and radially passing saidbodies within said chamber thereby exposing said bodies to said field;and collecting at least a portion of said bodies in a plurality saidgrooves at predetermined radial distances from said centrally disposedinlet means.
 7. A method according to claim 6 wherein said neutralpolarizable bodies comprise biological particles.